Offset core lifter apparatus



Feb. 18, 1969 CASPER ET AL 3,428,138

OFFSET CORE LIFTER APPARATUS Filed March 22, 1967 20 7 l 20:: 70C 205 LA I K :Zi I a 1 DIQ/ l k 4 P 2o l8 k /I l a I y N 4 L #84 23 m 23 INVENTORS R4) K. 6451 52 2 lab BY Ara/v42 Ava/arm;

lrrowvzrs United States Patent 8 Claims ABSTRACT OF THE DISCLOSURE Core barrel apparatus for drilling core from an earth formation, for receiving core as it is drilled, breaking the drilled core from the earth formation, and retaining the core as the core is retracted through the drill hole.

BACKGROUND OF THE INVENTION This invention relates to core drilling apparatus that has a core lifter mounted in a core lifter case for limited relative axial movement for breaking a core from an earth formation and retaining the core as the core is retracted through a drill hole.

In core drilling art, it is common to provide a drill stem having a core barrel outer tube at the inner axial end thereof with a core barrel inner tube within the outer tube for receiving the core as it is produced by the drilling operation. For purposes of breaking loose the drilled core from the earth formation, when the core barrel inner tube is filled, it is conventional to provide a core lifter case on the inner axial end of the core barrel inner tube, and a core lifter in the form of a small axially split ring having an exterior tapered or conical surface which bears upon a corresponding surface of the core lifter case and an interior surface for gripping the core. In the prior art the central axis of the internal bore of the core lifter case coincides with the central axes of the exterior surface of the core lifter case and the interior and exterior surfaces of the core barrel inner tube to which the core lifter case has been attached. The aforementioned type core lifter apparatus has been used both with wire line core barrel inner tube assemblies which are retractable independent of and through the drill stem, and core barrel inner tubes that are mounted in the drill stem in a manner such as disclosed in U.S. Patent 2,522,399 in which the entire drill stem has to be removed from the hole in the earth formation in order to retrieve the core. In order to retrieve the core, whether it be with wire line type equipment or the type in which the entire drill stem has to be retrieved, usually a substantial pulling force has to be exerted on the drill stem and thus to the core lifter apparatus in order to initially break the core after it has been drilled from the earth formation, this force being quite high in hard rock formations. After the core has been broken, thence the core barrel inner tube is retracted in order to retrieve the core.

SUMMARY OF THE INVENTION According to this invention, a core litter is mounted in a core lifter case for limited axial movement, the central axis of the core lifter being radially offset from the central axes of the core lifter case and the core barrel inner tube on which the core lifter case is mounted. That is, in order to substantially reduce the pulling force on the drill stem that is required to initially break the core from the earth formation, it has been found that by offsetting the internal bore portion of the core lifter case in which the core lifter is retained such that the central axis thereof is oifset a fraction of an inch from the central axis of the exterior and interior surfaces of the core barrel inner 3,428,138 Patented Feb. 18, 1969 ice tube and the exterior surfaces of the core lifter case, the pulling force required to break the core from the earth formation to which it is joined is substantially reduced from that which will be required if the interior surface of the core lifter case was not offset in the aforementioned manner.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated with reference to the drawings wherein:

FIGURE 1 is a fragmentary longitudinal cross-sectional view of the inner axial end of the drill stem and core barrel inner tube, together with core lifter apparatus attached to said inner tube;

FIGURE 2 is a transverse cross-sectional view of the structure shown in FIGURE 1;

FIGURE 3 is a longitudinal cross-sectional view of the core lifter case of this invention generally taken along the line and in the direction of the arrows 33 of FIG- URE 2; and

FIGURE 4 is an enlarged, fragmentary view of the structure of FIGURE 3 with a central portion thereof broken away.

DESCRIPTION OF THE PREFERRED EMBODIMENT For purposes of facilitating the description of the invention, the term inner refers to that portion of the drill stem, or of the assembly, or an element being described which in its position for use in the drill stem is located closer to core bit on the drill stem than any other portion of the apparatus being described, except where the term clearly refers to a transverse circumference, direction or diameter of the drill stem or other apparatus being described. The term outer refers to that portion of the drill stem, or of the assembly, or element being described which in its position for use in the drill stem is located closer to the mouth of the drill hole than any other portion of the apparatus being described, except where the term clearly refers to a transverse circumference, direction or diameter of the apparatus being described.

Referring now to FIGURE 1, there is illustrated the inner end portion of a drill stem 11, the portion illustrated constituting a portion of what is frequently referred to as the core barrel outer tube. To the inner end of the drill stern there is threadedly connected a rotary core bit 12 that is rotated by the drill stem to drill a core. The core bit has a central aperture 13 that is provided for boring the core in an earth formation 14. Located within the drill stem in a position to receive core as it is being drilled is a core barrel inner tube assembly having a core barrel inner tube 17, a core lifter case generally designated 18 being threadedly connected to the inner axial end of the inner tube and a core lifter 19 slidably retained in the core lifter case. It is noted that the only portion of the core barrel inner tube assembly illustrated is the inner axial end of the inner tube, the core lifter case and the core lifter; however, it is to be understood the core barrel inner tube assembly can be of a wire line type that is retractable through a drill stem, the core barrel inner tube assembly disclosed in U.S. Patent 2,829,868 being one example of such type; or a core barrel inner tube assembly that is not retractable independent of the drill stem, U.S. Patent 2,522,399 being one example of this type.

The outer end portion 21 of the core lifter case 18 has external threads that form a matching fit with theplane normal to the central axis LL of the core barrel inner tube interior and exterior surfaces, and the interior surface of portion 21, the beveled surface 24, the generally cylindrically exterior surface 18a and the conical or tapered surface 18b of the core lifter case. The recess 20 has an axial surface 20c that is centered with reference to axis LL, and a generally annular edge 20b that is slightly inclined relative to a plane normal to axis LL. Although edge 20b is illustrated as being inclined, it may be parallel to edge 20a.

The core lifter case has an axially elongated, gradually tapered axial inner surface 23 that at its outer axial end joins with the inner radial edge of surface 201; and at its opposite end joins with the beveled surface 24. The taper is such that the diametric dimension adjacent surface 24 is less than that at any axial position more closely adjacent groove 20. The central longitudinal axis MM of tapered surface 23 is offset a fraction of an inch from longitudinal axis LL, for example thousandths of an inch. Thus, at any plane normal to axis LL that is passed through surface 23 axially inwardly of groove 20, the maximum radial thickness of the wall of the casing at one angular position is substantially greater than that at a location 180 angularly spaced therefrom, while the radial thicknesses at angular positions 90 from the 180 position and either side thereof are equal and each are of a thickness intermediate that between the maximum thickness and the thickness of the 180 position. In FIGURE 4 arrows CC illustrate the maximum thickness portion of the casing at a given axial position along casing 18, while arrows DD shows a minimum thickness of the wall which is diametrically opposite portion CC.

To be mentioned is that the axis MM is parallel to axis LL, the spacing of axis MM from axis L-L being exaggerated in FIGURE 3 and FIGURE 4 for purposes of facilitating the description of this invention.

The core lifter case at its inner axial end has the beveled surface 24 that is of progressively increasing diameters in an axial direction toward the core bit aperture and a transverse outer beveled surface 18b of an angle of taper to form a mating fit with the inclined shoulder 12b of the core bit. Advantageously during the drilling operation, surface 18b is spaced relative to surface 12a such as illustrated in FIGURE 1; however, it is to be understood that insofar as the invention is concerned, these surfaces may be in abutting relationship at the time core is being drilled and appropriate fluid channels provided for conducting fluid from the annular space between the drill stem and the core lifter case to aperture 13 or to the core bit face 13b.

The core lifter case mounts for axial movement relative thereto, the core lifter 19 for grippingly holding and breaking a core as the drill stem is retracted. That is, the core lifter comprises a resilient split steel ring having a plurality of circumferentially spaced, axially elongated ribs 19a that are adapted to grip and break off the core and retain the core in the inner tube as the core barrel inner tube is retracted. The core lifter has a transverse outer axial conical surface 191) that is tapered to mate with the core lifter case surface 23. Further, the core lifter is longitudinally split at 29 so as to permit it to assume a shape of a smaller diameter or a larger diameter in a conventional manner.

The general radius of curvature X of the transverse inner edges of the core lifter ribs, when the core lifter abuts against edge 20a, or abuts against a stop ring (not shown) if such is provided in recess 20, is substantially the same as the inner radius of core lifter case surface 21 and the inner surface of inner tube axially outwardly of the core lifter case.

The structure of the apparatus of this invention having been described, the use thereof will now be set forth. For purposes of facilitating description of operation of the apparatus of this invention, it will be assumed that the drill stem is extended into a hole in an earth formation in a generally downward direction even though the use of the invention is not limited to drilling in a downward direction, and a core barrel inner tube assembly is located in the drill stem in a position to receive core as it is being drilled. Normally, at this time, the core lifter case is a substantial distance axially inwardly of recess 20 such as illustrated in FIGURE 1. Now the drill stem is moved axially inwardly to have the core bit face 13b abut against the annular groove in the earth formation and the core drilling operation is started whereby the cutting of core is begun. Because of the annular shape of the core bit, an ever deepening hole is cut with a rod like core being produced. As the drilling continues, the drill stem, including the core bit, move relative to the core whereby the core extends through the core bit aperture and thence into the core lifter case to abut against the adjacent surface of the core lifter. As the axial length of the core increases, the core lifter case moves relative the core lifter until the core lifter abuts against edge 20b (if no stop ring is provided, or if a stop ring is provided in recess 20 against the top ring). Thereafter, the core lifter case, the core lifter and the core receiving tube together move axially as a unit relative the core. In this connection, it is to be mentioned that in both conventional core drilling apparatus particularly of the type for deep hole drilling, a core barrel inner tube assembly is connected to a swivel so that the rotary motion of the drill stem is not imparted to the core barrel inner tube but rather the inner tube and core lifter case usually only move axially relative the core as the drill stem is rotated.

After core of desired length has been cut, for example, when a high pressure signal is provided at the surface through conventional structure, the drilling is stopped and the drill stem is pulled outwardly a short distance. Pulling the drill stem outwardly results in the drill stem moving axially outwardly relative the core lifter case until surface .12a abuts against surface 18b, provided appropriate conventional type of core drilling apparatus is used whereby the core lifter case is normally retained out of contact with the core bit. Assuming the core lifter case is movable relative the drill stern in the above manner, after surfaces 12a, 18b are in abutting relationship, further axially outward movement of the drill stem results in the core lifter case moving axially relative the core and the core lifter whereby through the drag of the core lifter on the core, the core lifter 19 is further axially spaced from groove 20 and is transversely compressed (due to tapered surfaces 23, 19b) to grippingly hold the core and break the core. In this connection it is to be noted that due to the offset of surface 23, the portion of the core lifter adjacent a maximum wall thickness (portion C--C) exerts a force against the core having a transverse component that is substantially greater than the transverse force at wall portion -D-D. As a result the core breaks with a substantially smaller pulling force than that which would be required if surface 23 were not offset from longitudinal axis LL as has been described heretofore. After the core has been broken, either the core barrel inner tube assembly is retracted relative the drill stem, or both the drill stem and core barrel inner tube assembly are retracted, depending upon the type of core drilling apparatus being used.

Desirably the offset of axis MM from axis LL is in a range of about 10 thousandths to 20 thousandths of an inch, the greater amount offset being preferred, but being limited by the minimum thickness of the case at dimension D'D that is required in order to maintain the structural strength of the core lifter case. Core lifter cases having greater differences between a maximum internal and external diameter in a plane normal to axis lP-L advantageously have offsets of greater dimensions.

As an example of one embodiment of the invention, but not otherwise as a limitation on the invention, the following dimensions are given. With the core lifter case being an axial length A of 2 inches, the outside diameter of surface 18a is 1.5 inches, the inside diameter of surface 21 is 1.364 inches, the inside diameter of the juncture of surface 24 with surface 2 3 is 1.374 inches, the angle of taper of surface 23 is about 2, the minimum axial length N of surface 23 as illustrated in FIGURE 3 is .974 inch, and the radial offset of axis MM from axis L-L is 15 thousandths of an inch.

'In order to more clearly show the advantages of this invention over the prior art, using the same drilling apparatus for drilling the core from the Barre Vermont Granite under the same drilling conditions, only the offset of axis M-M from axis L-L being varied between no offset to 20 thousandths of an inch offset. The pulling force required for breaking the core is set forth in the table as follows:

Offset (inches): Pulling force (pounds) 0 140 3 .005 140B .015 787 .020 46 8 What is claimed is:

1. For an axially elongated core receiving tube, core lifter apparatus comprising a core lifter case connected to one axial end of said core receiving tube to extend axially away therefrom, said core lifter case having a radially outer surface, a gradually tapered radially inner surface portion that diverges in a direction toward said core receiving tube, said outer surface and tapered inner surface portion each having a central axis, and a radially expandable core lifter mounted in said case for limited slidable movement between a position remote from said tube and a position more closely adjacent said tube, said core lifter having an exterior tapered surface portion that forms a close fit with said inner surface portion, characterized in that the core lifter case inner surface portion central axis is sufficiently radially offset from the outer surface central axis to substantially reduce the pulling force required to be exerted through the core lifter to break the core from that required with no radial offset.

2. The apparatus of claim 1 further characterized in that said core lifter case axes are parallel.

3. The apparatus of claim 1 wherein the core receiving tube has a central axis, and further characterized in that the core lifter case is mounted on the core receiving tube to have its outer surface central axis substantially coextensive with the core receiving tube axis.

4. The apparatus of claim 1 further characterized in that the inner surface portion central axis is offset from the outer surface axis at a minimum of about 10' thousandths of an inch.

5. For an axially elongated core receiving tube, core lifter apparatus comprising an axially core lifter case having an end portion threadedly connectable to one end of said tube, a radially outer surface and a transverse inner conical surface portion of a gradual taper of progressively increasing transverse dimension in an axial direction toward said end portion and a core lifter mounted in said core lifter case for limited axial movement, said core lifter having a transverse outer conical surface portion of a taper opposite the taper of the core lifter case in abutting engagement with said core lifter case conical surface portion, said core lifter case outer surface and core lifter conical surface portion each having a central axially extending axis, the improvement being that the central axis of the core lifter conical surface portion is radially offset from the central axis of the core lifter case outer surface an effective distance for substantially reducing the pulling force required to break the core from that required with no radial offset.

6. The apparatus of claim 5 further characterized in that said central axes are radially offset in a range of about .010 to about .020 of an inch.

7. The apparatus of claim 5 wherein the core receiving tube has a central axially extending axis, and further characterized in that the core lifter case is mountable on the core receiving tube to have its axis extend substantially coextensive with the core receiving tube axis and that the core lifter has axially elongated, circumferentially spaced, transverse inner ribs.

8. The apparatus of claim 7 further characterized in that said radial offset is about .015 thousandth of an inch.

References Cited UNITED STATES PATENTS 1,254,268 l/l918 Pickin 175-255 2,490,512 12/1949 'Deely 175- 255 X 2,522,399 9/ 1950 Pickard 175-255 2,708,104 5/ 1955 McAllister 1752 NILE C. BYERS, IR., Primary Examiner. 

